Hurricane Isaac hits Louisiana, driving dangerous storm surges

By: Dr. Jeff Masters , 2:27 AM GMT on August 29, 2012

Share this Blog
53
+

Hurricane Isaac is ashore over Southeast Louisiana, having officially crossed the coast on the Mississippi Delta 90 miles southeast of New Orleans at 7:45 am EDT on August 28. Isaac intensified right up until landfall, striking with 80 mph winds and a central pressure of 970 mb. The storm's large size and large 50 - 60 mile diameter eye kept the intensification rate slow today, but it came quite close to becoming a significantly more dangerous storm. That's because at landfall, Isaac was in the midst of establishing a small inner eyewall within its large 50-mile diameter eye, a very rare feat I've never seen before. Usually, when an eye first forms, it gradually contracts, eventually becoming so small that it becomes unstable. An outer concentric eyewall then forms around the small inner eyewall, eventually becoming the only eyewall when the inner eyewall collapses. But Isaac is a very unusual storm that has continually surprised us, and this inside-out concentric eyewall formation fits the storm's unusual character. The storm isn't in a hurry to move fully inland, and has slowed down to a crawl this evening. This will give the storm the opportunity to keep its center mostly over water a few more hours, and maintain hurricane strength into the early morning on Wednesday.


Figure 1. Radar reflectivity image from New Orleans as Isaac made landfall at 6 pm CDT August 28, 2012.

A dangerous storm surge event underway
Isaac is bringing large and dangerous storm surge to the coast from Central Louisiana to the Panhandle of Florida. At 10 pm EDT, here were some of the storm surge values being recorded at NOAA tide gauges:

6.2' Waveland, MS
9.9' Shell Beach, LA
3.0' Pensacola, FL
4.4' Pascagoula, MS
3.4' Mobile, AL

The 9.9' storm surge at Shell Beach, which is in Lake Borgne 20 miles southeast of New Orleans, exceeds the 9.5' surge recorded there during Category 2 Hurricane Gustav of 2008. Research scientists running a Doppler on Wheels radar located on top of the 16' levees in Plaquemines Parish near Port Sulphur, LA, reported at 8:30 pm EDT that a storm surge of 14' moved up the Mississippi River, and was just 2' below the levees. Waves on top of the surge were cresting over the west side of the levee. Needless to say, they were very nervous. Over the past hour, the surge has retreated some, and waves were no longer lapping over the top of the levee. This is probably due to the fact that we're headed towards low tide. A storm surge of 9.5' has moved up the Mississippi River to the Carrrollton gauge in New Orleans. This is not a concern for the levees in New Orleans, since the storm surge has now brought the river up to 2.5' above its normal water level, which was 7' low due to the 2012 U.S. drought. The highest rise of the water above ground level will occur Wednesday morning over much of Southeast Louisiana, Mississippi, Alabama, and the western Florida Panhandle, when the tide comes back in. It is clear now that this storm surge event will be as dangerous as that of Category 2 Hurricane Gustav of 2008. One piece of good news: NWS New Orleans successfully launched their 00Z balloon. However, their discussion noted the atmosphere is "saturated or nearly saturated" all the way up to 470mb, or 20,000 feet. Precipitable water was 2.76 inches, which will be ripe for extremely heavy rainfall.


Figure 2. Tide gauge data from Shell Beach, located on the south shore of Lake Borgne, just east of New Orleans. The green line shows the storm surge. The red line is the storm tide, the height of the water above Mean Sea Level (MSL.)

Portlight disaster relief charity responds to Issac
The Portlight.org disaster relief charity, founded and staffed by members of the wunderground community, have mobilized resources in advance of the arrival of Hurricane Isaac. Their crew, including 2 EMTs, is at the Biloxi Special Needs Shelter, and will be caring for shelter dwellers and doing rescues of people who call for help. Another team will be surveying all the shelters in the area to ensure that they are accessible to all people. You can donate to Portlight's disaster relief fund here.

I'll have more in the morning. Hunker down, New Orleans. It's going to be a long night.

Jeff Masters

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 1519 - 1469

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44Blog Index

Quoting Masquer08er:
I guess I have heard this (media shouldn't cover GOP convention during Isaac) so often on Twitter and social media that I'm over sensitive. This is the only site I can get weather discussion without politics. And, if politics gets brought in, virtually everybody stops it.
Understood. You are 100% right on that. I've seen it too.
Member Since: Posts: Comments:
Good morning, all. TWC said Baton Rouge will get hit hard. We're to get possible ITS winds later today and tonight. It appears the track has shifted a bit more west in the cone since last night?
Member Since: Posts: Comments:
1517. LargoFl
Member Since: Posts: Comments:
Isaac looks to be stationary again, Houma still on the western edge of the eye
Member Since: Posts: Comments:
1514. Jay5711
Quoting LATHUNDERBOLT:
hang on jason - if it keeps inching west along the coast it will be at vermilion bay a little later and lafayette will get "some" rain - (lafayette here too)


New Iberia here.. Winds out the northwest (were out the northeast last night), no rain as of yet.. But wind picked up lil from last night lot more gusts
Member Since: Posts: Comments:
Quoting GeorgiaStormz:


western eyewall opening up again...that side is really weak, new convection blowup staying on the east side of the storm and not wrapping around

Yeah, lot of dry air on the whole west side of the storm, if you're west of the eye you're gonna get very little rain.
Member Since: Posts: Comments:
Quoting weatherh98:
Landreu said new Orleans. Levees aren't overtopping or busting, that's when u run


I have a question, if power goes out where the "best pump system in the world is"(lack of better term d/t just woke up), how long will the back up generators work or aren't they powered with electricty? TIA Sorry if a stupid question
Member Since: Posts: Comments:
Quoting palmpt:


Taz... I am in New Orleans. Downtown. I Still have power, but most folks don't. I just drove around downtown. Trees are down all over the place... Two big ones across Poydras. Nola.com has excellent updating of the situation here. Down south of here, it's not good.

Your lucky. Look at this map.
Member Since: September 30, 2007 Posts: 9 Comments: 15932
Grand Isle and surrounding communities are taking a beating from Isaac.
Member Since: Posts: Comments:
1509. LargoFl
Quoting justsouthofnola:
Thanks for the radar... I live in Lockport, LA
Trees are down here an there no power few shingles missing off neighbors house
How fast is the storm moving?
not fast at all, just about sitting there, going to be a long day and night for you folks there
Member Since: Posts: Comments:
Quoting MAweatherboy1:
The eye is looking nice and round right now.

7AM:



Now:



western eyewall opening up again...that side is really weak, new convection blowup staying on the east side of the storm and not wrapping around
Member Since: Posts: Comments:
1507. ugajag
Looks like Mobile is about to get some serious weather..
Member Since: Posts: Comments:
Quoting HarleyStormDude52:
looks like it is moving due west...????????????


Looks to be meandering again.. Drift W maybe.
Member Since: Posts: Comments:
1505. GetReal
Well I guess that my post in reference to the coastal erosion and more open water to the south and Se of NOLA panned out. Isaac took advantage of those now open waters the past 16 hours to maintain strength, and get better organized.
Member Since: Posts: Comments:
The eye is looking nice and round right now.

7AM:



Now:

Member Since: Posts: Comments:
1503. emcf30
Quoting AussieStorm:

Where was that report from. Fox 8 has only reported 80mph at Lake P


Hey Aussie, here is one report from earlier this morning.

AccuWeather.com ‏@breakingweather At 1:40 AM CDT, a wind gust of 113 mph was measured at Belle Chasse Ferry Dock in Plaquemines Parish, LA.
Member Since: Posts: Comments:
Quoting HarleyStormDude52:
looks like it is moving due west...????????????
hugging the coast
Member Since: Posts: Comments:
isaccs.like.fay.on.steroids..good.luck
Member Since: Posts: Comments:
looks like it is moving due west...????????????
Member Since: Posts: Comments:
Quoting palmpt:


Taz... I am in New Orleans. Downtown. I Still have power, but most folks don't. I just drove around downtown. Trees are down all over the place... Two big ones across Poydras. Nola.com has excellent updating of the situation here. Down south of here, it's not good.



thanks for the update but i dont think you sould be out driveing a round did you see jim cantor why you where driveing down town?
Member Since: Posts: Comments:
el.salvador.earthquake.few.waves.came.inland.and.ki lled.rare.sea.turtle.nest...
Member Since: Posts: Comments:
I90 Biloxi
Member Since: September 30, 2007 Posts: 9 Comments: 15932
Quoting Waltanater:
Well, I do understand your point of view, but I honestly don't think he was going anywhere with it. The guy usually stays on topic here and is pretty cool. Not trying to defend, but maybe he didn't have anything else to compare it to...I don't know dude...l8ter.
I guess I have heard this (media shouldn't cover GOP convention during Isaac) so often on Twitter and social media that I'm over sensitive. This is the only site I can get weather discussion without politics. And, if politics gets brought in, virtually everybody stops it.
Member Since: Posts: Comments:
I can take a pic no way to post here
Member Since: August 6, 2011 Posts: 0 Comments: 226
Quoting MAweatherboy1:

That doesn't look unsafe at all...


fake... someone's holding his feet.
Member Since: Posts: Comments:
Long time lurker here. I have a family reunion in St. Lucia 9/1 to 9/6. What do the models say about 98L affecting the island during that period?
Member Since: Posts: Comments:
1492. Times2
Quoting leftlink:


Here's a radar loop. Is it calm enough to take a picture?




Leftlink can you provide a link to that radar loop. Thanks.
Member Since: Posts: Comments:
Morning All. Last run at intensification this morning, no longer an open center and appears to be stalled again?

Member Since: Posts: Comments:
Wow, just woke up to seeing the news that parts of Plaquemines Parish are up to 10-12 feet underwater..... so sad on the 7th anniversary.... have to run but keep safe everyone and good luck :(
Member Since: Posts: Comments:
Quoting presslord:


I'm not sure...but she started downloading them just as the storm came in...




next time you talk too pat ask if how many puppys she had and it they all made it ok
Member Since: Posts: Comments:
Quoting LargoFl:
Viewer sent this pic in to WDSU new orleans.......

That doesn't look unsafe at all...
Member Since: Posts: Comments:
1487. Jax82
First light on Isaac.

Member Since: Posts: Comments:
NWSNewOrleans ‏@NWSNewOrleans
Not sure about any instrument bias, but we got a report of 110 mph wind gust at Bayou Gauche in St. Charles Parish.
Member Since: September 30, 2007 Posts: 9 Comments: 15932
1485. palmpt
Quoting Tazmanian:



power is out too 70% of the city sol likey the phones are out too


Taz... I am in New Orleans. Downtown. I Still have power, but most folks don't. I just drove around downtown. Trees are down all over the place... Two big ones across Poydras. Nola.com has excellent updating of the situation here. Down south of here, it's not good.
Member Since: Posts: Comments:
Someone is walking their dog in the eye now!

LINKLink
Member Since: Posts: Comments:
1483. Times2
This thing is just not letting up. In Erath La. Storm creeping towards Vermilion Bay. If he goes south of here I will be shocked. I know that is not expected but Issac is not obeying the NWS.
Member Since: Posts: Comments:
1482. barbamz
Member Since: Posts: Comments:
Quoting Tazmanian:



thats asking that now ?? LOL



how many puppys did they all make it ok?


I'm not sure...but she started downloading them just as the storm came in...
Member Since: Posts: Comments:
Thanks for the radar... I live in Lockport, LA
Trees are down here an there no power few shingles missing off neighbors house
How fast is the storm moving?
Member Since: August 6, 2011 Posts: 0 Comments: 226
Quoting justsouthofnola:
Eye is currently over my house.... Not completely calm
Can I get a radar loop please. No power and phone radar loop only shows small amounts rain in the gom


Here's a radar loop. Is it calm enough to take a picture?



Member Since: Posts: Comments:
1478. LargoFl
Viewer sent this pic in to WDSU new orleans.......
Member Since: Posts: Comments:
Member Since: Posts: Comments:
1476. JasonRE
Will Lafayette LA see any rain? Also, is this thing possibly moving West? Lastly, could the real stuff hit Thurs now that it's moving so slow?
Member Since: Posts: Comments:
KFOL/KJUN HTV10.
Houma/Morgan city
Live stream.

Link
Member Since: September 30, 2007 Posts: 9 Comments: 15932
Quoting Chiggy:


Sorry not sure but TWC says it was a legitimate....


strengthening maybe?
not really strengthening but maybe tightening a tad..
Member Since: Posts: Comments:
Quoting presslord:
Spoke briefly to Pat's wife...they're alive and hunkered down....Anybody want a puppy?!



thats asking that now ?? LOL



how many puppys did they all make it ok?
Member Since: Posts: Comments:
Quoting Masquer08er:
I have had 24 hours of media coverage of Isaac and I watched the convention. There was programming other than the convention or Isaac, too. This is a political talking point. Go to MSNBC (WU's step cousin) to discuss it.
Well, I do understand your point of view, but I honestly don't think he was going anywhere with it. The guy usually stays on topic here and is pretty cool. Not trying to defend, but maybe he didn't have anything else to compare it to...I don't know dude...l8ter.
Member Since: Posts: Comments:
Thank you for that update!


Quoting presslord:
Spoke briefly to Pat's wife...they're alive and hunkered down....Anybody want a puppy?!
Member Since: Posts: Comments:
Quoting Jarhead6012:


Press have you heard anything new on Storm?


Yup,,,he's awake, grouchy...and about to start moving about and streaming...
Member Since: Posts: Comments:
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT WED AUG 29 2012

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON HURRICANE
ISAAC...LOCATED ON THE COAST OF SOUTHEASTERN LOUISIANA AND ON
TROPICAL STORM KIRK...LOCATED ABOUT 1435 MILES SOUTHWEST OF THE
AZORES.

SHOWER AND THUNDERSTORM ACTIVITY HAS INCREASED A LITTLE IN
ASSOCIATION WITH A BROAD AREA OF LOW PRESSURE ALONG A TROPICAL WAVE
LOCATED ABOUT 700 MILES WEST-SOUTHWEST OF THE CAPE VERDE ISLANDS.
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE CONDUCIVE FOR GRADUAL
DEVELOPMENT DURING THE NEXT COUPLE OF DAYS. THIS SYSTEM HAS A
MEDIUM CHANCE...50 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS IT MOVES WESTWARD TO WEST-NORTHWESTWARD AT
ABOUT 15 MPH.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.
Member Since: Posts: Comments:

Viewing: 1519 - 1469

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.